Effects of Blood Flow Restriction on O ₂ Muscle Extraction and O ₂ Pulmonary Uptake Kinetics During Heavy Exercise

This study aimed to determine the effects of three levels of blood flow restriction (BFR) on $\dot{V}{O}_2$ and O ₂ extraction kinetics during heavy cycling exercise transitions. Twelve healthy trained males completed two bouts of 10 min heavy intensity exercise without BFR (CON), with 40% or 50% BFR (BFR40 and BFR50, respectively). $\dot{V}{O}_2$ and tissue saturation index (TSI) were continuously measured and modelled using multiexponential functions. The time constant of the $\dot{V}{O}_2$ primary phase was significantly slowed in BFR40 (26.4 ± 2.0s; p < 0.001) and BFR50 (27.1 ± 2.1s; p = 0.001) compared to CON (19.0 ± 1.1s). The amplitude of the $\dot{V}{O}_2$ slow component was significantly increased ( p < 0.001) with BFR in a pressure-dependent manner 3.6 ± 0.7, 6.7 ± 0.9 and 9.7 ± 1.0 ml·min ⁻¹·kg ⁻¹ for CON, BFR40, and BFR50, respectively. While no acceleration of the primary component of the TSI kinetics was observed, there was an increase (p < 0.001) of the phase 3 amplitude with BFR (CON −0.8 ± 0.3% VS BFR40 −2.9 ± 0.9%, CON VS BFR50 −2.8 ± 0.8%). It may be speculated that BFR applied during cycling exercise in the heavy intensity domain shifted the working muscles to an O ₂ dependent situation. The acceleration of the extraction kinetics could have reached a plateau, hence not permitting compensation for the slowdown of the blood flow kinetics, and slowing $\dot{V}{O}_2$ kinetics.